Flip chips are packages containing integrated circuits and are typically composed of a semiconductor dip. The I/O contacts of the circuit are the input and output contact points for the circuit and are brought out to one face of the package. A substrate has contact bumps thereon which correspond to the I/O contact points on the package. The package is placed face down on one substrate with the contacts in corresponding position. When in position, the contacts are attached, as by reflow soldering. This type of flip chip attachment is convenient and reliable. The problem arises from the possibility that contaminants can get between the integrated circuit package and the substrate. Such contaminants could reduce the reliability of the circuitry. As a result of that possibility of contamination, flip chip integrated circuits on substrates are usually housed for protection. Housing, in turn, adds costs, increases the package size, and reduces the heat dissipation.
At present, some integrated circuits on substrates are protected from the environment by encapsulating them in synthetic polymer composition material or some other organic material. This is not suitable for radio-frequency circuits. Another way of protecting integrated circuits is to place them in a hermetically sealed container made of metal and/or ceramic. This method involves many additional parts and process steps. It adds weight, takes up space, and reduces heat emission.